The Great Filter: are we rare, are we first, or are we doomed?

Fermi’s Paradox (the fact that we never detected any sign of aliens even though, conceptually, life could be relatively common in the universe) has already been discussed in this blog, as new results come in about the rarity of life bearing planets, the discovery of new Earth-like planets, or even the detection of possible signs of aliens.

There are a number of possible explanations for Fermi’s Paradox and one of them is exactly that sufficiently advanced civilizations could retreat into their own planets, or star systems, exploring the vastness of the nano-world, becoming digital minds.

A very interesting concept related with Fermi’s Paradox is the Great Filter theory, which states, basically, that if intelligent civilizations do not exist in the galaxy we, as a civilization, are either rare, first, or doomed. As this post very clearly describes, one of these three explanations has to be true, if no other civilizations exist.

The Great Filter theory is based on Robin Hanson’s argument that the failure to find any extraterrestrial civilizations in the observable universe has to be explained by the fact that somewhere, in the sequence of steps that leads from planet formation to the creation of technological civilizations, there has to be an extremely unlikely event, which he called the Great Filter.

This Great Filter may be behind us, in the process that led from inorganic compounds to humans. That means that we, intelligent beings, are rare in the universe. Maybe the conditions that lead to life are extremely rare, either due to the instability of planetary systems, or to the low probability that life gets started in the first place, or to some other phenomenon that we were lucky enough to overcome.

It can also happen that conditions that make possible the existence of life are relatively recent in the universe. That would mean that conditions for life only became common in the universe (or the galaxy) in the last few billions years. In that case, we may not be rare, but we would be the first, or among the first, planets to develop intelligent life.

The final explanation is that the Great Filter is not behind us, but ahead of us. That would mean that many technological civilizations develop but, in the end, they all collapse, due to unknown factors (some of them we can guess). In this case, we are doomed, like all other civilizations that, presumably, existed.

There is, of course, another group of explanations, which states that advanced civilizations do exist in the galaxy, but we are simply too dumb to contact or to observe them. Actually, many people believe that we should not even be trying to contact them, by broadcasting radio-signals into space, advertising that we are here. It may, simply, be too dangerous.


Image by the Bureau of Land Management, available at Wikimedia Commons

3 thoughts on “The Great Filter: are we rare, are we first, or are we doomed?”

  1. I think the history of our planet argues for the rarity conclusion. Simple unicellular life seems to have arisen early in our planet’s history, but it took billions of years for complex life to arise, and of the estimated five billion species that have ever existed on the planet, only one seems to have achieved symbolic thought. It seems to follow that simple unicellular life may be pervasive, but complex life may be rare, and intelligent life may be profoundly rare.

    Of course, you could argue that basing conclusions on a sample of one is perilous, and I’d agree. It could mean the conclusions about simple and complex life are off. But the rarity conclusion for intelligence seems corroborated by the Fermi paradox. If civilizations are common, where is everyone?


  2. I can only assume that complex life is the Great Filter. It seems to be the only step in the evolution of us that life seemed to struggle with. And to explain just how dead the universe is it must be near impossible to get complex life. I don’t subscribe to intelligent life being rare because several animals are smarter than we give them credit for and it doesn’t seem like they had much trouble getting as intelligent as they are. Also, other species of humanoids on Earth have achieved intelligence to varying degrees. Even dolphins appear to be very intelligent and may have even discovered language and a means to pass on hunting techniques to the net generation just as humans had.

    So intelligence doesn’t seem to be all that improbable. But the leap to complex life taking almost 2 billion years IMO is the only thing that makes sense as the great filter. But it brings up other questions as to WHY that step is so rare and WHY it happened here.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: